AB-INITIO CHARACTERIZATIONS OF MOLECULAR-STRUCTURES, CONFORMATION ENERGIES, AND HYDROGEN-BONDING PROPERTIES FOR POLYURETHANE HARD SEGMENTS

Ab initio Hartree-Fock and MP2 calculations with 3-21 G and 6-31G* basis sets were conducted for a group of urethane model molecules and hydrogen-bonded dimers to study the intra- and intermolecular interactions for polyurethanes. Conformational structures and energies of internal bond rotations were calculated and compared with available experimental results. Three types of hydrogen bonds that formed between the urethane N-H group and (1) the urethane carbonyl oxygen, (2) the ester oxygen, and (3) the ether oxygen were studied. The vibrational frequency shifts of the N-H, C=O and C-O-C stretching modes computed for the dimers at the HF/6-31G* level qualitatively agree with the experimental observations of polyurethanes and support the assignment of the 3295-cm-1 band to the N-H stretching mode in the N-H...O-(ether) hydrogen-bonding structure.